System OFF mode but with 150ms consistent shoot seen in oscilloscope

[kathleenlai]

Hi Team,

I would like to know what does the system do after I call system off function as per below:

void PowerApp__EnterSleepMode(void)
{
    ret_code_t err_code;

    // Go to system-off mode (this function will not return; wakeup will cause a reset).
    err_code = sd_power_system_off();
    APP_ERROR_CHECK(err_code);
    return;
}

I have check through the oscilloscope to check how's the system react when system off mode.

I have a consistent pulse with Interval is now 150ms - 155 ms , the current peak is at 2.2mA. 

Is that normal? or Can anyone explain to me what will happen right after sleep when I connect NRF52840 to oscilloscope.

Im using SDK  16.0.0.

Thank you.

[Susheel Nuguru]

Hi,

there should be no power spikes of that magnitude in system_off mode. Either some external circuit to the chip is consuming the power or the chip has already woken up system off mode.

[kathleenlai]

Hi Susheel, would that be recharge pulse?

would it be caused by DCDC regulator / LDO regulator?

[Susheel Nuguru]

maybe at the time of wakeup , but not during active sleep.

[kathleenlai]

what do you mean by time of wakeup?

my pulse is consistent on going after sleep. 

[Susheel Nuguru]

I meant that the chip in itself should not consume any currents apart from the wakeup source configured. All clocks and most of the voltage regulators are switched off. Can you please try to reproduce this just on nordic DK excluding any external things you added. I suspect that this spike comes outside of nRF chip.

[kathleenlai]

I will flash into the nrf52840DK with the blinky example later on. will be back to you for the outcome. thank for the suggestiong,let's try out.